Chiral acylnitroso dienophiles 14, which were obtained from L-proline and from D-mandelic acid, reacted with cyclohexa-1,3-diene to give the expected diastereoisomers 15 and 16 (Scheme 2 and Table 1). The d.e. values for these Diels-Alder reactions were moderate; they are related to the molecular stiffness of the dienophiles. The absolute configuration of the major cycloadducts was interpreted in terms
Cycloaddition of chiral nitroso derivatives with cyclohepta-1,3-diene gave one single stereoisomer with an excellent selectivity. The structures including absolute configurations have been assigned by spectroscopy and X-ray crystallography. These studies have been applied to the total synthesis of the naturally occurring calystegine B2.
手性亚硝基衍生物与环庚-1,3-二烯的环加成反应产生了一种具有优异选择性的单一立体异构体。包括绝对构型在内的结构已通过光谱学和X射线晶体学确定。这些研究已经应用于天然存在的calystegine B 2的全合成。
Single and double asymmetric induction in Diels-Alder cycloadditions with chiral acylnitroso dienophiles
achiral 1-silyloxybutadiene 1a with the chiral acyinitroso dienophile 2a gave cycloadduct 4 in high diastereomeric excess (d.e. > 98 %), a result which is undoubtedly due to the C-2 symmetrical chiral dimethylpyrrolidine inductor. Excellent d.e. was also observed when the (R)-prolinol dienophile 2d was reacted with the chiral diene 1b (d.e. = 96 %), whereas cycloaddition of the (S) enantiomer 2e with 1b gave